The present invention relates to paving machines, and more particularly to screed assemblies for paving machines having a main screed portion and at least one screed extension movably connected to the main screed.
Screed assemblies 1 used with paving machines 2 to level paving material 9, typically asphalt, applied by the machine 2 onto a generally horizontal base surface 3 are well known, an example of such being depicted in FIG. 1. Further, screed assemblies 1 having both a main screed 4 and at least one extendible screed section 5 or screed extension 5 connected to the main screed 4 are also known. As a shown in FIG. 2, such a screed assembly 1 typically includes the main screed 4, often formed of two aligned sections (separate sections not shown), and at least one and generally two extendible screed sections 5 connected with the main screed 4. The screed extensions 5 are preferably movable with respect to the main screed 4, typically by means of a hydraulic cylinders (not shown) so as to either extend outwardly substantially beyond the outer ends 4a of the main screed 4 or retracted into centralized positions. Thus, the screed assembly 1 may be adjusted for use in paving base surfaces 3 of various widths.
Often, in material mats 7 formed using a screed assembly 1 having extendible sections 5, a pair of lines or streaks 8 appear in the mat 7 which are brighter in appearance or "shinier" than the remaining portions of the material mat 7 (FIG. 2). These streaks 8 appear in the sections of the mat 7 leveled by the regions of the screed assembly 1 where the screed assembly 1 transitions from the inner ends 5a of the screed extensions 5 to the outer ends 4a of the main screed 4. At least two factors are believed to be contribute to the appearance of the streaks 8. One factor is that fine particles of the paving material 9 tend to accumulate at the inner ends 5a of the extendible sections 5 during a paving operation, such that the streaks 8 are sections of the mat 7 formed with a higher concentration of fine-grained material. As finer particles are capable of being compressed more densely than larger grains, the finer particles thereby form areas that appear shinier than remaining portions of the mat 7.
Another factor that may cause or contribute to the formation of the streaks 8 is the fact that the outer sections 7a of the mat 7 are leveled (and thus compressed) by the screed extensions 5 prior to the inner, middle section 7b being leveled by the main screed 4. Thus, the outer edges of the inner mat section 7b are formed along a "dead zone" of already leveled and compacted material at the inner edges of the outer mat sections 7b. As such, there is a lack of interaction between the material particles in the adjacent regions 7a and 7b of the mat 7, which factor is also believed to lead to the formation of the streaks 8. Further, it may be that other, unknown factors contribute to, or may even be primarily responsible for, the appearance of the streaks 8 in the material mat 7.
Therefore, it is desirable to provide a screed assembly having a main screed and extendible screed sections that is capable of forming a material mat without any streaks. Further, it is desirable to provide a means for retrofitting existing screed assemblies to eliminate the above-discussed streaking